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Scheiner's sketches and writings

Rosa Ursina

Frontispiece of Scheiner's "Rosa Ursina", published in Bracciano between 1626 and 1630 [1].

Drawing shows apparent paths of sunspots across the solar disk, for two sets of observations taken six months apart.

Scheiner's helioscope, after a drawing in Scheiner's "Rosa Ursina".

Scheiner's Rosa Ursina, partly as a backlash following Galileo's condemnation, the massive volume (780 pages) did not draw very positive reviews following its publication, nor did it go down too well in history, largely because of the various vociferous attacks on Galileo scattered throughout Book I. The book was not without merit, however. In it Scheiner uses his observations of sunspot paths across the solar disk to convincingly demonstrate that the Sun's rotation axis is inclined with respect to the Earth's orbital plane. This observation was taken up as his own by Galileo in his Dialogues as a further argument for the heliocentric hypothesis, which was to further provoke Scheiner into accusations of plagiarism. In addition, the book has proven very useful as a store of sunspot data for to the period immediately preceding the Maunder minimum. Scheiner's later book, "Prodromus pro Sole Mobile", a rabid criticism of Galileo's 1632 Dialogues, was withheld from publication during Scheiner's lifetime, apparently because it was deemed overly distasteful by his ecclesiastic superiors.

The inclination of the Sun's rotation axis

One of a great many sunspot drawings in Scheiner's "Rosa Ursina", reproduced from The history of the discovery of the solar spots, in Popular Astronomy, 24, W.M. Mitchell, 1916. Based on such observations, Scheiner correctly concluded that the Sun's equatorial plane is inclined by 7° with respect to the ecliptic. This observation was taken up as his own by Galileo in his "Dialogue concerning the two chief world systems" as a further argument for the heliocentric hypothesis, which was to further provoke Scheiner into accusations of plagiarism.

Scheiner's helioscope

While Galileo largely abandoned systematic sunspot observations following the publication of his "Three letters on Solar Spots", Scheiner devoted himself fully to sunspot observations. He improved onthe projection method of Galileo and Castelli by designing a specialized telescopic solar projection instrument, which he called heliotropii telioscopici (helioscope being a rough contracted translation). This represents the earliest known equatorially mounted instrument.

Bibliography:

[1] Mitchell, W.M. 1916, The history of the discovery of the solar spots, in Popular Astronomy, 24, 22-ff.

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